Free cutting alloys



Patented Jan. 7, 1936 UNITED STATES PAT ENT fOFFlCE FREE CUTTING ALLOYS Louis W. Kempf and Walter A. Dean, Cleveland, Ohio, assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania c No Drawing. Application May 3, 1935, Serial No. 19,611 a v 2 Claims. (Cl. 75-1 This invention relates to aluminum base alloys out disadvantageously affecting the physical and it is particularly concerned withthose alloys properties of the alloy. containing silicon as a major alloy component. Our invention is predicated upon the dis- This application is a continuationin part of ccvery that the addition of lead and/or thallium our co-pending application, Serial No.689,880, to aluminum-silicon alloys containing from about filed September 18, 1933. Alloys disclosed but 3 to 15 per cent silicon greatly improves the manotclaimed herein are claimed in our abovechining quality oi! thistype of aluminum'alloy. mentioned co-pending application, Serial No. Theimprovement is especially marked in those 689,880, and in our co-pending applications, valloyscontaining from about to per cent of 10 Serial Nos. 19,607, 19,608, 19,609, 19',610," 19,61 2,1' "SiliQQIlifllhiCh have heretofore been particularly 10 19,613, 9,614, 19,615, and 19,616, filed Mayii, 1diflicult j to.ymachinehz-wwe have found that the 1935. 1 v additionof frOm abOutODS to 10 percent of lead Aluminum base alloys containing from about and/orfth'a'llium to-aluminum-silicon alloys im- 3 to 15 per cent of silicon have been .widely used parts a machinability' to the alloy-which rendersv in cast, extruded and wrought forms because of it adaptable to all ordinary machining-require- 15 such desirable'casting characteristics as fluidity ments. For the purpose of our invention, lead and low solidification shrinkage of the molten and thallium are substantially equivalent and alloy, combined with a good workability of the are consideredtoconstitute a class .of-elem'ents' solid metal; if ,a' wrought article is tobe made. 'with respect to their effect upon the machining The alloys also possessa low coeflicient or thermal quality of aluminum-silicon alloys. I

expansion and satisfactory Physical. properties, The improvement in machining characteristics particularly tensile-strength andelongation;; In referred to above may be broughtabout-by the spite of these advantageous propertiea thefield addition of between bout 0.05 and'lO per cent of of utility ofthese alloys has been 'res tri cted be-n lead 01 thallium to alumi um base ll y 6 cause of their. inherently -poor machining quality tam from about 3 W 15 p cent Silicon,

and consequent increased cost of finishing articles for many app a io s W P f r to 11 between of these alloys by machining operations such as about 1 and 5 per cent of either lead or thallium.

boring, drilling, shaping, planing, or l th -c t- The effect on machinability of these added ele ting. Difiiculty in machining is made evident ments is manifested by the smooth flow of chips through an excessive cutting tool wear which from the article beingmachined, the short break- 30 necessitates a frequent resharpening. Poor maable chips that are produced, the absence of chinability is also manifestedin arough irregular gelling unevenness of resulting n machined surface andthe tendency to form long irregul r Surface 01 (11111 pp r the chips that may foul the cutting tool or operating i c as in cutting spe d. which is p s b u e parts of the machine, Aluminum.'.5fljc0n alloys such favorable conditions. As an example of an are furthermore quite likely to have hard paralloy possessing these properties the following ticles of elementary silicon distributed through-' comp siti ay be cited: 12 per c n. out the alloy matrix which seriously interfere 4 P cent lead, balance, substantially-al.11111- with smooth cutting-of the article being maminumr; Y .v

40 chined. These diflicultiesare most readily ap- Lcfl- -flndl h ium m y n 011 3??? Bu 40 parent in machining operations conducted on a #1 9 5 n binary a u uml c n 1 y large scale such as the manufacture of pistons in' alloys containing copp mdfi um, for internalv combustion engineswh'er'e it has b ean the like inadditionto the silicon. founddesirable to use anexp'ensive cutting cti n i l ad nd hall immune the material to insurelong tool life "and'a sati acmachinabllity of such" alloys'appears' fofbe ,sub- 15 tory machined surface. stantially independent of the other alloying in- It is accordingly'one of the objects of our in-, gredients added te -alter the character of'the'basic mention to make 'aluminumrsilic'on alloys amenaluminum-silicon alloy. an illustration of Y able to machining operations on a large scale 'thej'beneflt derived from the use of lead orthalj. before referredxto. =lfil-speciilc purpose is to d 'iium in?alloysofithihaturepthe case of-an alloy used'in the manufacture or pistons forlinternal combustion engines may be cited. *An -alloy n? taining about 12.5 per cent of silicon, 1 percent of magnesium, 0.8 per cent of nickel, and 0.8 per 50 without encountering'the disadvantages hereinminis'h the irregularityjlr'i cutcaused by. h silicon particles and to producea'a'i smooth-ypleas ing surface on the machined article; Aiuithefj object is to accomplish the foregoing ends with-"t-cent of copper, balance aluminum, had greatly 55 improved machining quality after the addition of about 3 per cent of lead as compared to the same alloy containingno lead. Another example of the beneficial effect of lead on the machining characteristics of aluminum-silicon base alloys is found in an alloy containing about 5 per cent silicon, 0.7 per cent jcopper, and 0.3 per cent magnesium, the balance being aluminum. This alloy in cast form may be used for making cylinder heads for certain types of internal combustion engines. It is desirable that such a casting be readily machinable without diminishing the strength at ordinary or elevated temperatures. We have found that the addition of about 2.25 per cent of lead produces a marked improvement in machining quality without impairing any of the other desired properties of the alloy.

Lead and thalliummay not only be used separately in alloys of the type herein disclosed, but they may be efiectively employed in combination in certain applications. The two elements frequently co-act in an aluminum-silicon alloy to produce a degree of machinability not attained by an equivalent amount of either element alone. When so used in combination the total amount should not exceed 10 per cent and preferably less than 5 per cent is recommended. The relative proportions of. the two elements may be varied but approximately equal amounts of them generally give satisfactory results.

D For certain applications it has been found esirable to add other elements than lead and thallium which also serve to improve the machin- 7 ing quality of the alloys disclosed herein. The elements cadmium and bismuth belong to this group. A commercially useful group of alloys have been made up from compositions within the following range, silicon 3 to 15%, copper 0.1 to

5.0%, magnesium 0.1 to 1.5%, and one or more of 4 the elements lead, bismuth, cadmium, or thallium,

in amounts respectively as follows, lead 0.05 to' 10%, bismuth 1.5 to 6%, cadmium 1.5 to 6%, and thallium 0.05 to 10.0%. We have tested cast samples for tensile strength, per cent elongation and machining quality, on specific alloys within the above range, including the following alloys which may be regarded as representative.

(1) An aluminum base alloy containing 5.0% silicon, 1.2%. copper, 0.5% magnesium, and 4.0% lead, the balance being aluminum.

(2) An aluminum base alloy containing 5.0% silicon, 1.2% copper, 0.5% magnesium and 4.0% bismuth, the balance being aluminum.

(3) An aluminum base alloy containing-5.0%

silicon, 1.2% copper, 0.5% magnesium, and 4.0% cadmium, the balance being aluminum.

(4) An aluminum base alloy containing 5.0% silicon, 1.2% copper, 0.5% magnesium, 2.0% lead and 2.0% bismuth, the balance being aluminum.

(5) An aluminum base alloy containing 5.0% silicon, 1.2% copper, 0. 5% magnesium, 2.0% lead, and 2.0% cadmium, the balance being aluminum.

(6) An aluminum base alloy containing 5.0% silicon, 1.2% copper, 0.5% magnesium, 2.0% bismuth and 2.0% cadmium, the balance being aluminum.

(7) An aluminum base alloy containing 5.0% silicon, 1.2% copper, 0.5% magnesimn, 1.3% lead, 1.3% bismuth and 1.3% cadmium, the balance 5 being aluminum.

We have found that the above addition of lead.

bismuth, or cadmium markedly improves the machining properties of the aluminum-silicon-copper-magnesium alloy without materially afiecting w the, tensile strength or elongation. As in the case of alloys discussed hereinabove, we have also found that combinations of more than one of the free machining elements lead, cadmium, bismuth,

or thallium 'cause a greater improvement in ma- 15 chining properties than the same total amount of only one free machining element. By this we mean, as a specific example, that alloys 4, 5, 6, and 7 immediately above are superior in machining properties to alloys 1, 2, and 3, although in 20 all cases the total amount of free machining constituent is 4 per cent.

If total quantities of free machining constituents are larger than about 5%, there is a decrease in tensile strength, but the machinability is improved, which serves to compensate for the decrease in strength. In any event, the total amount of free machining elements should preferably not exceed about 10%.

The lead and-thallium may be most conven- 30 iently added to the molten aluminum-silicon alloy in solid metallic form. Other methods of making alloy additions practiced by those skilled in the art yield equally satisfactory results. If the amount of lead and thallium tobe added exceeds 35 about 1.5 per cent, the melt should be heated somewhat above ordinary temperatures and vigorously stirred to assure a unifo mixture. The method of adding lead and thallium to aluminum and its alloys 'here referred to is more fully de- 40 scribed in co-pending application, Serial No. 689;885 now Patent No. 1,959,029 gran ted May 15, 1934.

The term aluminum used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade.

to 15, per cent of silicon, about 0.1 to 5 per cent of 55 copper, about 0.1 to 1.5 per cent of magnesium and about 1.5 to 6 per cent of bismuth, the balance being aluminum.

2. An aluminum base alloy containing about 5 per cent of silicon, about 1.2 per cent of copper, so about 0.5 per cent of magnesium and about 4.0 per cent of bismuth, the balance being aluminum.

LOUIS W. KEMPF. WALTER A. DEAN. 

